This invention relates to a rotary jaw chuck for machine tools or the like with a detector for determining the presence of stock.
In machining operations involving bar stock or the like, the bar is typically fed through a work holder from one side so as to extend from the other side or end of the work holder, where the stock is machined. The feeding is done in steps, automatically, and the workpiece is gripped after each step or advance, rotated and machined. The work holder is required to hold and rotate the workpiece against the force developed during cutting or machining and adequate gripping depends upon sufficient bar stock remaining within the work holder after each advance. Thus, it becomes necessary to detect when the bar has become too short to be advanced and safely gripped to machine an additional part.
Detectors for determining the presence of stock for gripping are known, but have typically been mechanically complex or have required rotary joints or slip rings to bridge a connection between the rotary holder and a sationary detector and control, if the detectors are electrically or air operated. In certain collet type work holders the above problems have been circumvented with a detector sensitive to air pressure in a conduit of the work holder within which a stock detecting sensor moves to detect the presence of work gripped internally of the chuck body. In such an arrangement air is supplied from a stationary source when the work holder is stopped and pressure builds up in the supply passage if a workpiece blocks movement of the sensor. The pressure build up is sensed and permits continued operation.
It will be appreciated that detectors for present purposes must be rugged and simple enough to function under machining conditions, i.e., in the presence of chips, coolant, vibration, heat, and the like. They must also be reliable because of the safety hazard created when a workpiece is inadequately gripped. Where the stock is gripped beyond the chuck body, as in a jaw chuck, arranging a satisfactory location of and construction for the detector without interfering with the operating mechanisms and without wasting undue lengths of stock which could be adequately gripped becomes a problem.